Lithographic apparatus and device manufacturing method

ABSTRACT

A lithographic apparatus is disclosed. The apparatus includes an illuminator for conditioning a beam of radiation, and a first support for supporting a patterning device that serves to pattern the beam of radiation according to a desired pattern. The apparatus also includes a second support for supporting a substrate, a projection system for projecting the patterned beam onto a target portion of the substrate, and at least one gas generator for generating a conditioned gas flow. The gas generator includes a guiding element for guiding the gas flow to a lower volume generally located below a lower surface of the projection system and to a volume between the lower surface and the substrate. The guiding element directs the gas flow in a generally downward direction and then in a direction generally parallel to the lower surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority from U.S. ProvisionalPatent Application No. 60/571,534, entitled “LITHOGRAPHIC APPARATUS ANDDEVICE MANUFACTURING METHOD,” filed May 17, 2004, the content of whichis incorporated herein by reference in its entirety.

FIELD

The present invention relates to a lithographic apparatus and a devicemanufacturing method.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a target portion of a substrate. Lithographic apparatus can beused, for example, in the manufacture of integrated circuits (ICs). Inthat circumstance, a patterning device, such as a mask, may be used togenerate a circuit pattern corresponding to an individual layer of theIC, and this pattern can be imaged onto a target portion (e.g.comprising part of, one or several dies) on a substrate (e.g. a siliconwafer) that has a layer of radiation-sensitive material (resist). Ingeneral, a single substrate will contain a network of adjacent targetportions that are successively exposed. Known lithographic apparatusinclude so-called steppers, in which each target portion is irradiatedby exposing an entire pattern onto the target portion in one go, andso-called scanners, in which each target portion is irradiated byscanning the pattern through the projection beam in a given direction(the “scanning”-direction) while synchronously scanning the substrateparallel or anti parallel to this direction.

In the ongoing efforts for attaining higher resolutions at smallerimaging dimensions in lithographic systems, projection systems are usedthat have numerical apertures that are well above 0.8. These systemstend to be very bulky and wide in dimensions, in particular near thelower surface of the system where the radiation (light) exits theprojection system for illuminating a substrate. Furthermore, these highnumerical apertures have a working distance that is usually very small(only a few millimeters), which causes the projection system to beplaced very close to the wafer surface. As a result of this, inpractical setups, there is very little room provided for arrangementsthat are operative in the area between the lower surface of theprojection system and the substrate. One of these arrangements that areoperative in the above indicated area is an gas shower system that ispresent to condition the “gas” (which is usually a very fine conditionedcomposition of gases) in this area. This conditioning, among others, isnecessary for defining a stable gas environment so that interferometricmeasurement beams are unhindered by refractive index fluctuations. Thisis necessary for obtaining reliable (sub) nanometer measurements of theposition of the substrate in relation to the projection system, so thata pattern is reliably imaged at a predefined position of the substrate.

However, the above indicated developments of bulkier projection systemsand closer working distances thus make it difficult to position the gasshower system in such a way that this area as a whole is sufficientlyreached. In particular, due to the lower working distance and bulkierprojection system, there is virtually not enough room to place an gasshower system in such a way that the gas flow is sufficiently able tocondition the volume located below a lower plane of the machine setupabove the wafer table. Generally, such a lower plane may be formed bythe lowest plane of the projection system, which could be the exit planeof the lower lens. Otherwise this plane could be formed by the Z-mirrorthat is used in determining the z-height of the substrate to beilluminated.

SUMMARY

It is an aspect of the present invention to provide a lithographicsystem where the area below the projection system is better reached bythe gas shower system. To this end, the invention provides alithographic system that includes a radiation system for providing abeam of radiation; a first support structure for supporting a patterningdevice, the patterning device serving to pattern the beam of radiationaccording to a desired pattern; a second support structure forsupporting a substrate; a projection system for projecting the patternedbeam onto a target portion of the substrate, the projection systemincluding a lower surface for defining a working distance to thesubstrate; and at least one gas generating structure for generating aconditioned gas flow in a volume extending between the lower surface andthe substrate, the gas generating structure including a guiding elementfor guiding the gas flow to a lower volume generally located below thelower surface of the projection system, wherein the guiding elementdirects the gas flow from a generally downward direction to a directiongenerally parallel to the lower surface of the projection system.

According an embodiment, a guiding element guides the gas to a directionalong the lower surface of the projection system in a volume below theprojection system, thus optimizing the gas flow below the lower surfaceof the projection system, while the gas shower system can be positionedat least partly generally above a lower surface of the projectionsystem.

The guiding element may include a guiding surface oriented generallyperpendicular to a direction of incidence of the gas flow. Further,preferably, the guiding element directs the gas flow from a generallydownward direction from the upper to the lower volume, to a directiongenerally parallel to the lower surface of the projection system. Inthis way, the volume directly under the projection system can be reachedby the gas flow, that flows from the side downwards alongside theprojection system.

In an embodiment, the upper volume is sectioned by a casing thatencloses the projection system, wherein the guiding element is a cut outsection in the casing enclosing the projection system, for guiding thegas flow along the cut out section towards the lower volume. Thus, inthis way, by these cut out sections, a passage to the gas flow isprovided generally through the lower part of the projection system. Inparticular, the cut out section may include a generally downwardoriented slope extending to a generally flat lower surface of theprojection system. It is noted that a further benefit is derived fromthese cut-out sections since it distances the outer surface of theprojection system from the gas flow. In this way, the gas is lessaffected by the surface temperature of the projection system, which mayslightly differ from the conditioned temperature of the gas flow.

In an embodiment, the guiding element may be a deflecting panel that ispositioned to deflect the gas stream towards the lower volume. Here, thedeflecting panel may be shaped to provide a first downward flowdirection, and a second flow direction, that is generally parallel to alower surface of the projection system to deflect the gas flow accordingto the Coanda effect. This effect was discovered in 1930 by Henri-MarieCoanda who observed that a stream of gas (or a other fluid) emergingfrom a nozzle tends to follow a nearby curved surface, in particular ifthe curvature of the surface or angle the surface makes with the streamslant.

In an embodiment, the panel may be adjacent to a Z-mirror, defining thelower surface of the projection system. Further, the panel may include asuction opening included with a suction device to pull the gas flowtowards a generally horizontal flow. Such a suction may support theCoanda effect to “pull” the gas flow close to the curve of the panel.Additionally, preferably, the panel may include a recess is for guidingan interferometric beam in the recess.

In an embodiment, the structure for generating the conditioned gas flow(also shortly indicated as “gas shower”) may include a second guidingelement that is arranged in the gas flow to locally deflect the gasflow, in order to arrive a split gas flow that is partially directed tothe upper volume and partially to the lower volume. The gas flowvelocities in the split gas flows may differ. In particular, a part ofthe gas flow that is directed to the volume of the projection system mayhave a higher velocity than the part of the gas flow that is directed tothe lower volume. In such a configuration, the high speed gas flowpenetrates more easily to the volume directly below the lower surface ofthe projection system. Hence, the velocity distribution induces a changein pressure distribution that is operative to provide a guiding effect,by convection, so that the direction of the more downward velocity gasflow is also oriented more parallel to the lower surface of theprojection system.

The second guiding element may be formed by a plurality of slatsarranged in the gas flow.

To be employed in a setup near the projection system, the panel mayinclude a first radial shape oriented generally radially when viewedfrom a center of the projection system, and a second tangential shapeoriented generally partly around the projection system, and wherein thegas generating structure is arranged to provide a gas flow directedgenerally perpendicular to the panel structure.

The guiding element may be physically attached to a metro frame carryingthe projection system. The gas generating structure may be attached to abase frame, mechanically decoupled from the metro frame.

In an embodiment, a lithographic apparatus is provided. The apparatusincludes an illuminator for conditioning a beam of radiation and a firstsupport for supporting a patterning device. The patterning device servesto pattern the beam of radiation according to a desired pattern. Theapparatus also includes a second support for supporting a substrate, anda projection system for projecting the patterned beam onto a targetportion of the substrate. The projection system includes a lower surfacefor defining a working distance to the substrate. The apparatus alsoincludes at least one gas generator for generating a conditioned gasflow. The gas generator includes a guiding element for guiding the gasflow to a lower volume generally located below the lower surface of theprojection system and to a volume between the lower surface and thesubstrate. The guiding element directs the gas flow in a generallydownward direction and then in a direction generally parallel to thelower surface of the projection system.

In an embodiment, a lithographic apparatus is provided. The apparatusincludes an illuminator for conditioning a beam of radiation, and afirst support for supporting a patterning device. The patterning deviceserves to pattern the projection beam according to a desired pattern.The apparatus also includes a second support for supporting a substrate,and a projection system for projecting the patterned beam onto a targetportion of the substrate. The projection system includes a lower surfacefor defining a working distance to the substrate. The apparatus alsoincludes at least one gas generator for generating a conditioned gasflow in a volume extending between the lower surface and the substrate.The gas generator is arranged to generate a gas flow that is directedtowards a volume of the projection system above the lower surface. Thegas generator includes a guiding element for guiding the gas flow to alower volume generally located below the lower surface of the projectionsystem.

In an embodiment, a device manufacturing method is provided. The methodincludes patterning a beam of radiation, projecting the patterned beamof radiation onto a target portion of a substrate with a projectionsystem, generating a conditioned gas flow in a volume extending betweena lower surface of the projection system and the substrate, and guidingthe gas flow in a generally downward direction and then to a directiongenerally parallel to the lower surface of the projection system.

In an embodiment, a device manufacturing method is provided. The methodincludes patterning a beam of radiation, projecting the patterned beamof radiation onto a target portion of a substrate with a projectionsystem, generating a conditioned gas flow in a volume extending betweena lower surface of the projection system and the substrate, directingthe gas flow towards a volume of the projection system above the lowersurface, and guiding the gas flow to a lower volume generally locatedbelow the lower surface of the projection system.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,liquid-crystal displays (LCDs), thin film magnetic heads, etc. Theskilled artisan will appreciate that, in the context of such alternativeapplications, any use of the terms “wafer” or “die” herein may beconsidered as synonymous with the more general terms “substrate” or“target portion”, respectively. The substrate referred to herein may beprocessed, before or after exposure, in, for example, a track (a toolthat typically applies a layer of resist to a substrate and develops theexposed resist) or a metrology or inspection tool. Where applicable, thedisclosure herein may be applied to such and other substrate processingtools. Further, the substrate may be processed more than once, forexample, in order to create a multi-layer IC, so that the term substrateused herein may also refer to a substrate that already contains multipleprocessed layers.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of 365, 248, 193, 157 or 126 nm) and extremeultra-violet (EUV) radiation (e.g. having a wavelength in the range of5–20 nm), as well as particle beams, such as ion beams or electronbeams.

The term “patterning device” used herein should be broadly interpretedas referring to a device that can be used to impart a projection beamwith a pattern in its cross-section such as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the projection beam may not exactly correspond to thedesired pattern in the target portion of the substrate. Generally, thepattern imparted to the projection beam will correspond to a particularfunctional layer in a device being created in the target portion, suchas an integrated circuit.

The patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions; in this manner, thereflected beam is patterned. In each example of patterning device, thesupport structure may be a frame or table, for example, which may befixed or movable as required and which may ensure that the patterningdevice is at a desired position, for example, with respect to theprojection system. Any use of the terms “reticle” or “mask” herein maybe considered synonymous with the more general term “patterning device”.

The term “projection system” used herein should be broadly interpretedas encompassing various types of projection system, including refractiveoptical systems, reflective optical systems, and catadioptric opticalsystems, as appropriate, for example, for the exposure radiation beingused, or for other factors such as the use of an immersion fluid or theuse of a vacuum. Any use of the term “lens” herein may be considered assynonymous with the more general term “projection system”. Inparticular, the projection system may include a plurality of partlystacked optical elements which may be transmissive (lenses), orreflective (mirrors). Generally, the projection system is configured insuch a way the radiation exits from the projection system through alowest optical element, defining a lower surface of the projectionsystem. More in particular, the lower surface of the projection systemis defined by the lowest surface that is present above the scan regionof the substrate. In a number of configurations, this lowest surface maybe formed by a Z-mirror that is used for controlling the Z-position ofthe support structure that supports the substrate.

The illumination system may also encompass various types of opticalcomponents, including refractive, reflective, and catadioptric opticalcomponents for directing, shaping, or controlling the projection beam ofradiation, and such components may also be referred to below,collectively or singularly, as a “lens”.

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables (and/or two or more mask tables). In such“multiple stage” machines the additional tables may be used in parallel,or preparatory steps may be carried out on one or more tables while oneor more other tables are being used for exposure.

The lithographic apparatus may also be of a type wherein the substrateis immersed in a liquid having a relatively high refractive index, e.g.water, so as to fill a space between the final element of the projectionsystem and the substrate. Immersion liquids may also be applied to otherspaces in the lithographic apparatus, for example, between the mask andthe first element of the projection system. Immersion techniques arewell known in the art for increasing the numerical aperture ofprojection systems.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 is a schematic view of a lithographic apparatus according to anembodiment of the invention;

FIG. 2 is a schematic view of an embodiment of a guiding element a gasshower of the apparatus of FIG. 1;

FIG. 3 is a plan view of a portion of the apparatus, including aprojection system, of FIG. 1 when viewed from below;

FIG. 4 is a cross-sectional view taken along line X—X in FIG. 3;

FIG. 5 shows a simulation of an embodiment according to the arrangementshown in FIG. 4;

FIG. 6 is a schematic illustration of gas flow in a portion of theapparatus of FIG. 1 when the guiding element is absent;

FIG. 7 is a schematic illustration of gas flow in the portion of theapparatus shown in FIG. 6 when the guiding element is present;

FIG. 8 shows an embodiment of a gas shower of the apparatus of FIG. 1;and

FIG. 9 shows an embodiment of a gas shower of the apparatus of FIG. 1.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic apparatus according to anembodiment of the invention. The apparatus includes: an illuminationsystem (illuminator) IL for providing a projection beam PB of radiation(e.g. UV radiation or EUV radiation); a first support structure (e.g. amask table) MT for supporting a patterning device (e.g. a mask) MA andconnected to a first positioning device PM for accurately positioningthe patterning device with respect to item PL; a substrate table (e.g. awafer table) WT for holding a substrate (e.g. a resist coated wafer) Wand connected to a second positioning device PW for accuratelypositioning the substrate with respect to item PL; and a projectionsystem (e.g. a refractive projection lens) PL for imaging a patternimparted to the projection beam PB by the patterning device MA onto atarget portion C (e.g. comprising one or more dies) of the substrate W.The term substrate table as used herein can also be considered or termedas a substrate support. It should be understood that the term substratesupport or substrate table broadly refers to a structure that supports,holds, or carries a substrate.

As here depicted, the apparatus is of a transmissive type (e.g.employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g. employing a programmable mirror array of a type asreferred to above).

The illuminator IL receives a beam of radiation from a radiation sourceSO. The source and the lithographic apparatus may be separate entities,for example, when the source is an excimer laser. In such cases, thesource is not considered to form part of the lithographic apparatus andthe radiation beam is passed from the source SO to the illuminator ILwith the aid of a beam delivery system BD including, for example,suitable directing mirrors and/or a beam expander. In other cases thesource may be integral part of the apparatus, for example, when thesource is a mercury lamp. The source SO and the illuminator IL, togetherwith the beam delivery system BD if required, may be referred to as aradiation system.

The illuminator IL may include an adjusting device AM for adjusting theangular intensity distribution of the beam. Generally, at least theouter and/or inner radial extent (commonly referred to as σ-outer andσ-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator can be adjusted. In addition, the illuminator ILgenerally includes various other components, such as an integrator INand a condenser CO. The illuminator provides a conditioned beam ofradiation, referred to as the projection beam PB, having a desireduniformity and intensity distribution in its cross section.

The projection beam PB is incident on the mask MA, which is held on themask table MT. Having traversed the mask MA, the projection beam PBpasses through the lens PL, which focuses the beam onto a target portionC of the substrate W. With the aid of the second positioning device PWand position sensor IF (e.g. an interferometric device), the substratetable WT can be moved accurately, e.g. so as to position differenttarget portions C in the path of the beam PB. Similarly, the firstpositioning device PM and another position sensor (which is notexplicitly depicted in FIG. 1) can be used to accurately position themask MA with respect to the path of the beam PB, e.g. after mechanicalretrieval from a mask library, or during a scan. In general, movement ofthe object tables MT and WT will be realized with the aid of along-stroke module (coarse positioning) and a short-stroke module (finepositioning), which form part of the positioning device PM and PW.However, in the case of a stepper (as opposed to a scanner) the masktable MT may be connected to a short stroke actuator only, or may befixed. Mask MA and substrate W may be aligned using mask alignment marksM1, M2 and substrate alignment marks P1, P2.

The depicted apparatus can be used in the following preferred modes:

1. In step mode, the mask table MT and the substrate table WT are keptessentially stationary, while an entire pattern imparted to theprojection beam is projected onto a target portion C in one go (i.e. asingle static exposure). The substrate table WT is then shifted in the Xand/or Y direction so that a different target portion C can be exposed.In step mode, the maximum size of the exposure field limits the size ofthe target portion C imaged in a single static exposure.

2. In scan mode, the mask table MT and the substrate table WT arescanned synchronously while a pattern imparted to the projection beam isprojected onto a target portion C (i.e. a single dynamic exposure). Thevelocity and direction of the substrate table WT relative to the masktable MT is determined by the (de-)magnification and image reversalcharacteristics of the projection system PL. In scan mode, the maximumsize of the exposure field limits the width (in the non-scanningdirection) of the target portion in a single dynamic exposure, whereasthe length of the scanning motion determines the height (in the scanningdirection) of the target portion.

3. In another mode, the mask table MT is kept essentially stationaryholding a programmable patterning device, and the substrate table WT ismoved or scanned while a pattern imparted to the projection beam isprojected onto a target portion C. In this mode, generally a pulsedradiation source is employed and the programmable patterning device isupdated as required after each movement of the substrate table WT or inbetween successive radiation pulses during a scan. This mode ofoperation can be readily applied to maskless lithography that utilizesprogrammable patterning devices, such as a programmable mirror array ofa type as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

An embodiment of the invention is illustrated in FIG. 2. In FIG. 2, aprojection system 1 that is located at a working distance 2 above asubstrate 3 is depicted. The projection system 1 typically includes aplurality of partly stacked optical elements (not shown) which may betransmissive (lenses), or reflective (mirrors). Generally, theprojection system 1 is configured in such a way that the radiation exitsfrom the projection system through a lowest optical element that definesa lower surface 4 of the projection system 1. In particular, the lowersurface 4 of the projection system 1 is defined by the lowest surfacethat is present above the scan region of the substrate 3. In a number ofconfigurations, this lowest surface may be formed by a Z-mirror, as willbe further illustrated with reference to FIG. 3, that is used forcontrolling the Z-position of the substrate 3. In this embodiment, theinvention uses the Coanda effect for guiding a gas flow 5S emerging froma nozzle 6 of a gas generating structure 7, shortly called a gas showeror a gas generator, along a curved surface of a guiding element 8. Inthis way, the guiding element 8 guides the gas flow 5S to a lower volumegenerally located below the lower surface 4 of the projection system 1from a generally downward direction to a direction generally parallel tothe lower surface 4 of the projection system 1. Although FIG. 2 showsthe gas stream to be directed initially alongside the guiding element 8,as will be shown with reference to FIG. 7, alternatively, the gas stream5S may be directed generally under an angle to the guiding surface andgenerally horizontal with respect to the lower surface 4, or slightly atan angle, to be deflected downwards by the guiding element 8 in agenerally downward direction.

FIG. 3 depicts a plan view of the arrangement below the projectionsystem 1 depicted when viewed from below. The projection system 1 isshown as a generally round hull 9 that encloses a plurality of stackedoptical elements (not shown), and wherein a cut out section 10 isprovided in the hull enclosing the projection system, for guiding thegas flow along the cut out section and to the volume generally centralbelow the projection system 1. These cut-out sections 10 will be furtherdescribed with reference to FIG. 9. FIG. 3 also shows the guidingelement 8 for guiding the gas to a direction along the lower surface ofthe projection system 1. The guiding element 8 may be in the form of adeflecting panel that is positioned to deflect the gas stream towardsthe lower volume. The function of this panel has been illustrated withreference to FIG. 3. A Z-mirror 11 is oriented generally along a middleline of the arrangement. The function of the Z-mirror 11 is for forminga reference frame for determining the Z-position (height) of substrate3. In the depicted embodiment, parallel to the Z-mirror 11 and below it(so in the view of FIG. 3 illustrated in front of the Z-mirror),interferometric reference beams 12 are radiated from an interferometricmeasuring unit 13 for determining X- and/or Y-positions of the stagethat supports the substrate (not shown). Generally speaking, the volumethat needs to be conditioned is formed along and enclosing the path ofthe interferometric beams 12, for reasons of controlling the refractiveindex of the gas. Thus, it can be seen that the volume central to theprojection system (indicated by dotted lines), due to its low positionrelative to the substrate, may be difficult to condition, since it islocated farthest from the gas shower 7. To be able obtain the centralparts below the projection system 1, the gas shower 7 has a generallytwo part main direction of gas output: one first direction Qsubstantially perpendicular to the Z-mirror 11 and a second direction Roriented from the perimeter of the projection system 1 in a generallyradial direction toward the centre of the projection system 1. To guidethe gas flow towards these directions, a first part 8 a of the guidingelement 8 is aligned in along the Z-mirror 11 generally radially whenviewed from the center of the projection system 1, and a second part 8 bis oriented generally partly around the projection system 1 in atangential form. Additionally, the gas shower 7 is arranged to provide agas flow (Q, R) directed generally under an angle α to the guidingelement 8.

FIG. 4 is a cross-sectional view of FIG. 3 along the line X—X. As isshown in FIG. 4, the guiding element 8 is adjacent to the Z-mirror 11that defines the lower surface of the projection system 1. Using theguiding element 8, the gas flow stays in contact with the guidingsurface of the guiding element 8 and is able to reach the region 14below the Z-mirror 11, in particular the region positioned opposite tothe guiding element 8 where the temperature and density are to be keptstable for the interferometric beams. An arrow Y is depicted to identifya suction opening that is included with a suction device to pull the gasflow towards a generally horizontal flow. Such a suction may have anadditional guiding effect supporting the Coanda effect.

A simulation with the angle α=68° is shown in cross-sectional view inFIG. 5. A lighter part 15 of the gas flow indicates a higher velocity.In this arrangement, the gas flow curves well around the guiding element8 and reaches the relevant area 14 without disturbances.

FIG. 6 and FIG. 7 are illustrated in combination to visualize the effectof the guiding element 8 in absent (FIG. 6) or present (FIG. 7) state.As can be seen in FIG. 6, the outlet 16 of gas shower 7 is directedtowards a volume of the projection system above the lower surface ofZ-mirror 11. In absent state of the deflector, the gas flow 5S bouncesagainst the side wall of the Z-mirror 11 and would cause disturbancesand unconditioned gas, in particular in region 14. However, as can beseen in FIG. 7, due to the guiding element 8, the gas flow 5S is guidedtowards region 14 by following the contour of the guiding element 8 dueto the Coanda effect.

FIG. 7, also shows a recess 21 directly adjacent to the Z-mirror 11 forguiding an interferometric beam 17. The Z-mirror 11, guiding element 8,and projection system 1 are mounted on a metro frame 22 that isdynamically separated from a base frame 18, which is grounded to theearth and carries the gas shower 7.

FIGS. 6–8 also show that the gas shower 7 includes a second structure19, 20 for deflecting partially the gas flow 5T to a lower volume belowthe lower surface of Z-mirror 11. This second gas flow 5T may have a gasflow velocity that is lower than the velocity of the 5S gas flow. Theflow is split by a slat 19, or vane, that defines the upper outlet 16.This slat 19 is formed to provide an accelerating effect to the gasflow, in combination with upper guiding surface 20. To provide aconsistent gas flow S, a plurality of slats, or vanes, may be formed inthe gas flow for providing an more optimum guiding effect to the gasflow. In this arrangement, the 5S gas flow is directed to be deflecteddownwards by the guiding element 8 in a generally downward direction. Itis noted that FIG. 8 is illustrated without the guiding element 8 butwith the slat 19 for providing an accelerated gas stream S.

FIG. 9 shows a side view of the lower region of the projection system 1,that includes a plurality of stacked optical elements (not shown). Theview of FIG. 9 is depicted generally along a path of the interferometricbeams 12 of FIG. 3. By providing cut outs 10, the gas flow reaches thevolume more central to the projection system 1 more easily. The cut outsection 10 includes a generally downward oriented slope 21 extending toa generally flat lower surface of the projection system. This surface isarranged to coincide with the reference surface of the Z-mirror 11 (notshown). In addition, by providing the cut-outs, the temperature from theprojection system 1 is less strongly transmitted to the gas flow flowingunderneath it, resulting in a better conditioned gas flow in therelevant volume including the interferometric beams 12. These beams areillustrated to reflect to a substrate support 22 for supporting thesubstrate 3 depicted in FIG. 2.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. The description is not intended to limit theinvention.

1. A lithographic apparatus comprising: an illuminator for conditioninga beam of radiation; a first support for supporting a patterning device,the patterning device serving to pattern the beam of radiation accordingto a desired pattern; a second support for supporting a substrate; aprojection system for projecting the patterned beam onto a targetportion of the substrate, the projection system comprising a lowersurface for defining a working distance to said substrate; and at leastone gas generator for generating a conditioned gas flow, said gasgenerator comprising a deflecting panel adjacent to a Z-mirror thatdefines the lower surface of the projection system for deflecting saidgas flow to a lower volume generally located below the lower surface ofsaid projection system, wherein said deflecting panel is shaped toprovide a first downward flow direction, and a second flow directionthat is generally parallel to a lower surface of the projection systemand to guide the gas flow along a surface of the deflecting panel.
 2. Alithographic apparatus according to claim 1 wherein said deflectingpanel comprises a suction opening comprised with a suction device topull the gas flow towards a generally horizontal flow.
 3. A lithographicapparatus according to claim 2, wherein said deflecting panel comprisesa recess for guiding an interferometric beam in said recess.
 4. Alithographic apparatus according to claim 1, wherein said deflectingpanel comprises a first radial shape oriented generally radially whenviewed from a center of the projection system, and a second tangentialshape oriented generally partly around said projection system, andwherein said gas generator is arranged to provide a gas flow directedgenerally perpendicular to said deflecting panel.
 5. A lithographicapparatus according to claim 4, wherein said gas generator furthercomprises a first section for providing a gas flow generallyperpendicular to said radial shape of said panel, and a second sectionfor providing a gas flow generally perpendicular to said tangentialshape of said deflecting panel.
 6. A lithographic apparatus according toclaim 1, wherein the gas flow is guided along the surface of thedeflecting panel according to the Coanda effect.
 7. A lithographicapparatus according to claim 1, wherein said guiding element isphysically attached to a metro frame carrying said projection system,and wherein said gas generator is attached to a base frame that ismechanically decoupled from said metro frame.
 8. A lithographicapparatus comprising: an illuminator for conditioning a beam ofradiation; a first support for supporting a patterning device, thepatterning device serving to pattern the beam of radiation according toa desired pattern; a second support for supporting a substrate; aprojection system for projecting the patterned beam onto a targetportion of the substrate, the projection system comprising a lowersurface for defining a working distance to said substrate; and at leastone gas generator for generating a conditioned gas flow, said gasgenerator comprising a first guiding element for guiding said gas flowto a lower volume generally located below the lower surface of saidprojection system and to a volume between said lower surface and saidsubstrate, wherein said first guiding element directs the gas flow in agenerally downward direction and then in a direction generally parallelto said lower surface of the projection system; and a second guidingelement that is arranged in the gas flow to locally deflect and splitthe gas flow so that the gas flow is partially directed to said volumebetween said lower surface and said substrate, and partially directed tosaid lower volume.
 9. A lithographic apparatus according to claim 8,wherein the gas flow that is directed to said volume between said lowersurface and said substrate has a higher velocity than the gas flow thatis directed to said lower volume.
 10. A lithographic apparatus accordingto claim 8, wherein said second guiding element comprises a plurality ofvanes arranged in the gas flow.
 11. A lithographic apparatus accordingto claim 8, wherein said first guiding element is physically attached toa metro frame carrying said projection system, and wherein said gasgenerator is attached to a base frame that is mechanically decoupledfrom said metro frame.